class Layer:
    def __init__(self):
        #列向量
       self.x = None
       self.y = None
    def forward(self,x):
        #返回输出
        # return self.y
        pass
    def backward(self,y_gradient,learning_rate):
        #返回损失函数对于输入的导数
        # return self.x_gradient
        pass
